Ceramic heaters and igniters are well known and have been in use for many years. For example, ceramic igniters are being used extensively for igniting gas in appliances such as clothes dryers, stoves, ovens, water heaters, furnaces, pool heaters, etc. Heaters and/or igniters are also widely used for operating compression type engines or diesel engines. These heaters commonly referred to as glow plugs are installed in the engines wherein a portion of the heater extends into the combustion chamber to transfer heat to the fuel-air mixtures contained in the cylinder.
Ceramic igniters require a variety of performance requirements. For example, high speed or fast time to-temperature that is the time required to heat an element from room temperature to a temperature required for the ignition of a gas/air mixture. Another requirement for igniters is durability i.e. to operate for extended periods of time without being replaced.
A composite monolithic element for use as a hot surface igniter is disclosed in a U.S. Pat. No. 6,328,913 of Shaffer et al. As disclosed therein a hot surface igniter includes first and second regions or layers. The first region or layer comprises a low pressure ejection molded mixture of silicon carbide and silicon nitride particles or other compatible mixes which will alter processing as a resistor. The resistor includes two cold portions and a hot portion intermediate thereof. The second region or layer also includes an ejection molded mixture of silicon carbide and silicon nitride particles or other appropriate mixture, while the second layer contains the same or similar compounds as the first, the ratios of the compounds differ so that after processing it acts as an insulator and as a support for the first layer. These first and second layers are bonded together to form a joint free mechanically continuous structure and densified.
A more recent patent of mine, U.S. Pat. No. 6,610,964 relates to a multi-layer ceramic heater for igniting fuel in a diesel engine having an electrode, an insulative layer disposed over the electrode, a resistive layer disposed over the insulative layer at the tip of the heater and a conductive layer covering the insulative layer and extending from the resistive layer over the insulative layer to the base of the heater. A substantial proportion of the volume of resistive layer is located in close proximity to the tip of the heater. The resistive layer has a positive temperature coefficient (PTC) of electrical resistance and preferably a portion of the electrode is variably resistive for self-regulation purposes. Due to the geometry of the resistive layer and the variable resistive characteristics of the resistive layer and the electrode, the heater is well suited for applications that require quick start heating as well as good after glow properties or prolong heating at high temperatures.
Notwithstanding the above, it presently believed that there is a need and a potential commercial market for a multi-layer ceramic heater/igniter. There should be a need and a commercial market for such igniters because they have unique electrical properties and quick start-up from room temperature to ignition temperature. Further, such igniters are durable and capable of operating for extended periods of time without being replaced. Such igniters are also capable of being manufactured at competitive costs.